1. Field of the Invention
Carbides and nitrides of many transition elements provide a great diversity of desirable properties; hardness, conductivity of electricity and heat; catalytic and electrocatalytic activity. In addition, many of the carbides and nitrides are highly refractory, being chemically inert and stable to exceedingly high temperatures. The carbides and nitrides tend to have high melting points so as to be capable of maintaining a solid phase in a wide variety of systems requiring elevated temperatures. Because some of the carbides and nitrides are hard, they are useful for grinding or in conjunction with other materials for grinding.
In many of the applications of carbides and nitrides it is desirable to have a high specific surface area, Sg. This is particularly true where the carbide or nitride serves as a catalyst or is involved in a system requiring a large contact area, as for example the interaction between a gas phase and a solid phase. There exist certain phases of these carbides which are thermodynamically stable only at very high temperatures and are not expected to form at low temperatures. High temperatures cause loss of surface area by sintering. Production of these materials at low temperature would therefore constitute a major advance in materials technology.
2. Description of the Prior Art
Descriptions of conventional carburizing and nitriding processes may be found in Kieffer and Schwarzkopf, Hartstoffe und Hartmetalle, Springer-Verlag, Vienna, 1953; Kieffer and Benesovsky, Encyclopaedia of Chemical Technology, 2nd ed. Vol. 4, p. 70; Vol. 13, p. 814; Wiley (Interscience), New York, 1964; Juza, Nitrides of Metals of the First Transition Series, in Advances in Inorganic Chemistry and Radiochemistry, Vol. 9, Academic Press, New York and London, 1966; Kosolopova, Carbides, Plenum Press, New York, 1971; and Toth, Transition Metal Carbides and Nitrides, Academic Press, New York and London, 1971. References concerned with the production of high surface area catalysts include Bohm and Pohl, Troisiemes Journeer Internat. D'Etude des Piles a Combustible, p. 183, P.A.E., Bruxelles, 1969; Sokolsky et al., Elektrokhimiiya 8:1745 (1972) and Svata and Zabransky, Z. Colln. Czech. Chem. Commun. 39:1015 (1974). Improved processes for enhanced surface area tungsten carbide may be found in Ross and Stonehart, J. Catal. 48:42 (1977) and Mozulewskii et al., Kinetika i Kataliz 18:767 (1977). Imura et al., Preparation of Catalysts II, p. 627, Elsevier Scientific Publishing Co., (1979), describe the preparation of high specific surface area molybdenum oxycarbides.
Face-centered cubic carbides (FCC) .alpha.MoC.sub.1-x and .beta.WC.sub.1-x are first described in Clougherty et al., Nature (1961) 191:1194, and in Sara, J. Amer. Ceram. Soc. (1965) 48:251, respectively. The former is described in detail in Rudy et al., Trans. AIME (1967) 239:1247. These Mo and W carbides are thermodynamically stable only above 1650.degree. and 2525.degree. C. They can be obtained by quenching metal-carbon mixtures from these high to low temperatures very rapidly. This technologically awkward method suffers from formation of low-temperature phases as impurities. Methods for producing the carbides and their microhardness are reported by Samsonov et at., Fizika i Khimiia Obrabotki Materialov, 123 (1975) and BakadZakhryapin et al., Fiz. Metal. Metalloved. (1966) 21:782. Superconducting properties are reviewed by Willens et al., Phys. Rev. (1967) 159:327.